This invention relates to injection syringes and patient monitoring devices, and in particular to an apparatus for electronically recording capacitance-based measurements of doses of an agent delivered with an injection syringe.
In recent years, the value of keeping electronic medical records in place of paper records has been widely recognized in the health care industry. The use of electronic medical records allows health care providers and patients to store, retrieve, and share medical information with considerably more ease and accuracy. The sharing of medical information is particularly important in treatment programs involving the injection of insulin, human growth hormone, or other medications.
Typically, these injections are performed using disposable syringes. Unfortunately, no adequate apparatus exists that measures and electronically records dose information from a disposable syringe. As a result, the patient or health care worker performing the injection is burdened with the task of injecting the dose and then manually recording the dose amount in a log book.
Because of the frequency of such injections, often several times a day for diabetics, it becomes difficult for a patient to keep accurate records. Indeed, studies have shown that a patient""s own records and recollections are often incomplete and inaccurate. Additionally, a patient may intentionally cheat while making self-recorded entries in an attempt to create a log book that will please his or her doctor. In the long-term this makes patient monitoring extremely difficult and jeopardizes the treatment program, possibly even endangering the patient""s life.
Attempts have been made at developing electronic management systems for assisting patients in self-administered drug programs. For example, U.S. Pat. No. 5,019,974 issued to Beckers describes a hand-held, microprocessor-based recorder that interfaces with a master computer. The patient enters therapy information into the recorder via a keyboard. The recorder includes a display for displaying treatment therapy guidelines to the patient. The recorder also has a blood glucose meter for recording the patient""s blood glucose levels.
The recorder described by Beckers does not automatically measure and record dose information from a disposable syringe. After injecting a dose, the patient must manually enter the dose information into the recorder using switches or keys. Although this is an improvement over keeping written records on paper, the effectiveness of the drug program is still limited by the patient""s recollections and recordings, which are unreliable.
Attempts have also been made at developing devices that deliver a predetermined dose of medication and record the dose amount. For example, U.S. Pat. No. 5,176,502 issued to Sanderson et al. on Jan. 5, 1993 describes a syringe pump for expelling a preset dose of medication from a syringe. The syringe pump includes a syringe retainer for holding the syringe and a driver for engaging the plunger of the syringe. An electric motor pushes the driver and plunger into the syringe barrel to expel the medication.
The syringe pump further includes a monitoring circuit for monitoring the motion of the driver during the delivery of the medication. The monitoring circuit includes a linear potentiometer having an electrically conductive strip of resistive material. The resistive material is positioned such that it engages an electrical contact of the driver. The position of the electrical contact on the resistive strip varies the voltage of the monitoring circuit, thus indicating the position of the plunger inside the barrel. A microprocessor receives voltage signals from the monitoring circuit and compares the voltage signals to preprogrammed signals to determine if the plunger displacement corresponds to correct displacement for delivering the preset dose. A control mechanism connected to the microprocessor regulates the driver""s movement to ensure the preset dose of medication is delivered.
Although the syringe pump described by Sanderson does allow electronic recording of dose information, it is only designed to deliver medication directly into an intravenous line. It is not designed to inject a patient directly nor can it measure and record a dose from a syringe unless the syringe pump pushes the plunger. Consequently, the syringe pump is of little use to a health care worker who must inject a patient directly, or to an outpatient who must follow a self-injection treatment program.
Another device for injecting a preset dose of medication and for recording the injected dose is disclosed in U.S. Pat. No. 4,950,246 issued to Muller on Aug. 21, 1990. Muller describes a battery-operated injection pen having a pump rod driven by an electric motor. The electric motor is controlled by an electronic control unit that includes a microprocessor with a memory for storing dose information. The injection pen further includes a sensor connected to the control unit for electrically determining the position of the pump rod, and thus the amount of medication injected.
Although the injection pen described by Muller measures and electronically records dose information, it has several disadvantages that have precluded its widespread use. The injection pen is an expensive device requiring complicated electronic equipment to deliver and record doses. Moreover, because the injection pen integrates a syringe and electronic recorder into one device, it is not disposable. The patient must use it repeatedly for each injection, even after the injection pen has been contaminated with blood. Consequently, the injection pen does not provide an inexpensive, convenient, or hygienic solution to patients wishing to measure and electronically record injected dose information.
U.S. Pat. No. 4,853,521 issued to Ronald Claeys on Aug. 1, 1989 presents a programmable, intelligent reader unit which receives and records drug data using hand-held or fixed scanners. The scanners read bar codes in place on syringes, ampules, flow meters, etc. In addition, this intelligent reader allows the user to weigh a syringe before and after injection to determine and record the administered amount of medicine. Dosage data logged in this manner can be displayed or printed out in the form of a record.
Operating the device described by Ronald Claeys requires many complicated steps of weighing syringes, scanning in bar codes, etc. The complexity of the required procedures as well as the high cost of the apparatus have precluded its widespread use. Additionally, the device cannot be easily carried by the user for recording doses while away from the health care facility or home. Thus, no inexpensive apparatus exists for determining and electronically recording dose information from a disposable syringe. Further, no such apparatus exists that is both simple in operation and easily carried by a user.
It is a primary object of the present invention to provide an apparatus for capacitively determining and electronically recording an injection dose delivered from a disposable syringe. It is another object of the invention to provide an apparatus that may be easily operated and carried by a user. A further object of the invention is to suit the apparatus to diabetic patients, and to diabetes home care in particular. It is yet another object to provide an apparatus facilitating automated paperless data processing, from the measurement performed by the patient to the recording at the clinic. These and other objects and advantages will become more apparent after consideration of the ensuing description and drawings.
An apparatus for capacitively measuring and electronically recording a dose delivered using a syringe comprises: a holder for receiving and holding a syringe in a measurement position; a capacitive element coupled to the holder and enclosing the syringe such that a capacitive response of the capacitive element is indicative of the dose when the syringe is in the measurement position; a measuring device connected to the capacitive element for measuring capacitive responses of the capacitive element; and a recording device connected to the measuring device for recording a dose datum indicative of the capacitive response and thus indicative of the dose.
Preferably, the holder comprises a well laterally enclosing the syringe when the syringe is in the measurement position. The capacitive element is then coupled to the well such that at least one electrode of the capacitive element laterally encloses the syringe when the syringe is in the measurement position. In one embodiment, the capacitive element is defined between the liquid held in the syringe and an external electrode situated outside the syringe. A needle contact coupled to the holder is then used to establish electrical communication between the measuring device and the liquid, through the syringe needle, when the syringe is in the measurement position. In another embodiment, the capacitive element is defined between first and second electrically conducting longitudinal plates coupled to the holder, electrically insulated from each other, and situated opposite each other relative to the syringe.
In yet another embodiment, the capacitive element is situated entirely within the syringe. Two coaxial cylindrical electrodes, one near the inside surface of the syringe barrel and the other near the outside surface of the syringe plunger, are connected to input and output terminals on the outside of the syringe barrel. The housing comprises a contact field coupled to the outside of the housing. The contact field comprises an input contact for contacting the input terminal, and an output contact for contacting the output terminal. The input and output contacts are connected to the measuring device.
A port connected to the recording device is used to download data stored in the recording device to an external storage or communication device such as a host computer. Also connected to the recording device is a testing device for testing a physical condition of the patient and generating condition data representative of the physical condition. The recording device records the condition data. Preferably, the testing device is a blood glucose meter and the physical condition is the patient""s blood glucose level. A display connected to the measuring device is used to display recorded doses and blood glucose levels to the patient. A computing device is connected to the recording device. The computing device computes dose data from measured capacitive responses and stored calibration data, for storage in the recording device. Dose data preferably comprises administered doses. The calibration data, stored in a calibration memory device, is indicative of the correspondence between capacitive responses and dose data for the particular syringe used by the patient. The calibration data generated by measuring capacitive responses for the entire range of potential liquid quantities in the syringe, and recording the correspondence between liquid quantities and capacitive responses.
A housing encloses the measuring and recording devices, and preferably encloses and magnetically shields the capacitive element. The holder is mechanically coupled to the housing. The housing is sufficiently compact to be hand-held and carried by a user. The capacitive element preferably consists of a single capacitor, and the capacitive response preferably comprises the capacitance of the capacitor. In an alternative embodiment, the capacitive element comprises plural longitudinally-spaced capacitors, and the capacitive response comprises an capacitive response pattern.